Ovomancy

Ovomancy was a type of divination that involved cracking open eggs and observing which way the yolks fell. Robert Hilliard, a RavenclawPrefect in the 1990s, informed first years who had just been Sorted into Ravenclaw that this was not considered an unusual pastime within the House. In fact, according to him, not only would other Ravenclaws have no trouble with someone "spend[ing] [their] days and nights" practicing ovomancy in a corner of the common room, but one would "probably find a few people to help."

It is also said that "Gryffindors have been known to make jokes about Ravenclaws who have developed an interest in Ovomancy."[1]